Pilot studies by the author have suggested that there is an intmate connection between lateral inhibition and the tuning of spatial frequency channels in human vision. This investigation will attempt to provide an average quantitative picture of the receptive field characteristics of the neural units comprising a single channel. It will demonstrate some of the differences in the organization of spatial frequency analysis under photopic and scotopic conditions. Finally the possibility that the commonly used spatial frequency adaptation paradigm contains a substantial artifact due to after-images will be studied, in detail.